Topic: Resurrection of a cb750 K6 (update 9/28/12)

[lucky]

Don't listen to the upiddy K0 people, the K6 is best...

I just think that the KO owners had to grab onto something because their bikes had none of the improvements.

The K8 had all the improvements.

[hoodellyhoo]

The K8 had all the improvements.

With none of the style.......


I kid, I kid

[dhall57]

Don't listen to the upiddy K0 people, the K6 is best...

Mark you hurt my feelings, I know I've got a KO now, but you must of forgot I still have your K6's twin brother at my house also.

[Markcb750]

Oh.. ... I forgot K0 owners are also sensitive...sorry

[hoodellyhoo]

Had some time to putz with the bike. My original plan was to change the oil, put on my 350 tank, and jump the bike with my 350 battery just to see if it would start. I never got quite that far. I did test the electrics with the 350 battery and everything seems to be okay. I even got the bike to turn over a few times until the battery went flat. 

I swapped out the jet-black oil with a whatever 10w40 I had around. No new filter (yet, might get one today).

I discovered some weird green stuff in the float bowls for #2 and #3. The jets seem a little plugged in those carbs too so I doubt the bike would have started. In the end I decided just to pull the airbox, carbs, and insulators so I can begin working on them.



A look in the carbs revealed the stock 105 main jets and 40 slow jets, so that's good.

Finally I decided I wanted to take a look at the points. These are covered by the crash bar so I decided to take them off. I started working on the left side but the will require the removal of the exhaust to come off and nothing I tried would get the rusty exhaust to budge so I gave up and worked on the right side. There the crash bars came right off and revealed that the points look almost brand new! only a small amount of pitting that I need to file off. Even all of the adjustment screws looked perfect so maybe the whole points plate was changed recently.

While I was down there by the points I couldn't help but stare at the motor. You have to admit, it's one damn good looking motor. It looks like one big, solid, muscular chunk of metal. It seems to convey all of it's internal attributes (reliability, power, etc.) through its outward appearance. I like the look of some of the other japanese inline fours as well, but the cb750 was the first and is still the best.



Next time I work on the bike I would like to get the exhaust off for a thorough cleaning/polishing and maybe start cleaning the carbs.

[lucky]

You cannot just "file off " pitted points. They must be replaced.

The pitted points can fire in the peaks and valley of the points and therefore a thickness gauge will not work anymore.
If you do not believe me then adjust the points with a thickness gauge after you have filed them and check the dwell. See what I mean?

Also even if you did that the dwell can be off because the phonellic block of the points can be worn down and  and also cause the dwell time to be too low.

It is not unusual for points to look new and actually be worn out.

The problem with all of these 30 year old Honda cb 750s is not the mileage but the years they have sat. The steel parts will be ok but not the seals. Valve guide seals get hard and cam chain roller rubber wheels get rock hard. the rubber o rings in the cylinder base too. There is one member of this forum who decided to just run his CB750 after replacing fluids etc, and later on a oil change found bits of those rubber cam chain rollers almost completely covering the oil sump screen.

I think you will be taking the entire bike apart and restoring it and then next summer you will really enjoy having a "new" bike.

Check the electrical plug- in recepticles too as many cb750's this age have rotten plastic electrical connections.

Looks like the first thing to do is build yourself a wooden work bench along one of those walls even if it is only 24 inches wide. It will provide a place to put your parts while you rebuild the bike this winter. Keep things up off of the floor.

You have a good bike with many nice parts to work with. The end result will be very good.

[hoodellyhoo]

I spent most of my time today sorting an organizing my parts collectionand cleaning my new work area. I found a few 350 leftovers that I can use on the 750. As I've said I'm trying to save money wherever I can on this bike. I found the SCI master cylinder parts I had on the 350 for a short while but replaced with OEM honda parts because of faulty machining on the SCI plunger. I think I will take the rubber bits from the nearly-new SCI kit and put those into the 750 master once I take it apart for cleaning.

I put the carb insulators and airbox boots in my paint can of xylene/wintergreen oil for softening. I did this on my dad's K2 and it worked pretty well except the parts seemed to slowly harden up again over the course of a month. To try and keep this from happening again I added more wintergreen oil since apparently that is what soaks into and stays in the rubber, making it soft again.

On the subject of hard rubber bits, I once read that one reason these things get hard is because of fuel vapors. It must be true because some of the air horns in the airbox were soft on one side and hard on the other.

Soaking in the brew. I'll check them after a couple days. The insulators will probably go longer than the airbox boots.


My better organized workspace. My wife's stepdad teaches tech ed and gave me the old table

[hoodellyhoo]

You cannot just "file off " pitted points. They must be replaced.

Let me clarify: the points no different than the new pair on my 350 after a few hundred miles. I will file them and use them as-is.

I am still considering dropping the oil pan. I did it on the 350 and it wasn't too bad. Cheap way to get a better assessment of the motor's condition.

[hoodellyhoo]

I pulled the airbox boots today and they were floppy and swelled. We'll see how they are in a couple weeks once they dry out and shrink a little. I think I'll soak my 350 airbox parts as long as I'm at it since those boots have shrunk a little and don't seal as well anymore.

I also bought a buffing kit today so I can try polishing the cases with a drill. That way I won't have to remove them.

[Johnie]

Keep us informed on the airbox rubbers. I replaced the ones on the K3 as they were so hard and shrunk. I still have them and might give the Wintergreen a try in the future.

[hoodellyhoo]

Keep us informed on the airbox rubbers. I replaced the ones on the K3 as they were so hard and shrunk. I still have them and might give the Wintergreen a try in the future.

Will do. It will be a while before I can make a deffinitive conclusion. The rubbers on the K2 got harder over a couple of months. Granted, they didn't return to the rock-hard state they were before any treatment but I want these things to stay super-pliable. Hopefully the extra intergreen does the trick. Seems to have worked for other people.

[hoodellyhoo]

Today I spent 45 minutes doing what I thought would take about 10. All the airbox parts and rubber pieces I've been working on lately were all quite dirty so I decided to clean them up. Unfortunately all the dirt was quite caked on and required hard scrubbing to remove (hence the reason it took longer than I expected).



I'm still going to go back and remove all the surface rust off of the hardware. The airbox plastic has discolored a little bit so I might try rubbing on some peanut oil to bring back the shiny black. I'm also going to need a new airbox basket. Mine is falling apart.

Here's where my rubber parts are flexibility-wise. We'll see if they stay that way over the winter.

[dhall57]

Hoo, If your getting a new air box housing seal it's a pain in the A$$ to get installed and in place and everything back together. Maybe you know a trick, but took me forever and a few @*&@ words along the way too  

[Johnie]

I used a small screwdriver to help get it in by working around it and it went in pretty easy.

[Artf0rm]

Prayer said, small 2 stroke sacrificed to CB gods.  You should be good to go.

Looks like a great find.  I'll be waiting to see what happens when you crank it up.

[mrjack55]

You cannot just "file off " pitted points. They must be replaced.

The pitted points can fire in the peaks and valley of the points and therefore a thickness gauge will not work anymore.
If you do not believe me then adjust the points with a thickness gauge after you have filed them and check the dwell. See what I mean?

Also even if you did that the dwell can be off because the phonellic block of the points can be worn down and  and also cause the dwell time to be too low.

It is not unusual for points to look new and actually be worn out.

The problem with all of these 30 year old Honda cb 750s is not the mileage but the years they have sat. The steel parts will be ok but not the seals. Valve guide seals get hard and cam chain roller rubber wheels get rock hard. the rubber o rings in the cylinder base too. There is one member of this forum who decided to just run his CB750 after replacing fluids etc, and later on a oil change found bits of those rubber cam chain rollers almost completely covering the oil sump screen.

I think you will be taking the entire bike apart and restoring it and then next summer you will really enjoy having a "new" bike.

Check the electrical plug- in recepticles too as many cb750's this age have rotten plastic electrical connections.

Looks like the first thing to do is build yourself a wooden work bench along one of those walls even if it is only 24 inches wide. It will provide a place to put your parts while you rebuild the bike this winter. Keep things up off of the floor.

You have a good bike with many nice parts to work with. The end result will be very good.

Hey, nice pic Lucky.  What I don't even get a nod, a quick credit, nothing?  You tell a story about another member, and then lift my picture to illustrate it?  You really are a class act.

[hoodellyhoo]

Got a few hours of work in yesterday. I started my cleaning up all of the intake clamps and hardware with some steel wool and my dremel. Then I assembled it for now. I still need to get a new airbox gasket. I was considering making my own with either some foam or neoprene, which I can get at my work, but I think oem would probably be best. My other revelation is that I should spend the Harbor Freight gift cards I have on one of their ultrasonic cleaners. I'm tired of cleaning every small piece of hardware by hand. Then I could use it on carburetors too.

edit: just looked at the reviews online and it seems they don't do carbs well. Plus the usual HF quality issues.



The other thing I did was disassemble the carbs. I guess these K6's had a simple emissions control device I never knew about. There's a cap with a tab over the air screws. The tab hits another tab on the carb body, only allowing one turn of adjustment.



It appears someone has been into these carbs before, though luckily they weren't too ham-fisted. None of the screws had any signs of tampering but there were a few things off.

The slide holder thingy on carb #1 was really bent upwards. I also couldn't remove one of the screws holding it down so it looks like I'm not taking it apart. I'll just bend the holder back down. Hopefully I don't have to change the needle clip position



Besides having some of the main jets look a little buggered, three of the four carbs had a metal washer under the float valve seat instead of the stock fiber washer so I assume the float valves were replaced at some point.



Other than than the bent holder and some really stubborn float shafts the disassembly went fine. I might get around to starting the cleaning this afternoon or tomorrow.

[Greggo]

Nice work Hoo!  I'm at the carb stage of my K6's rebirth as well. 

[mrjack55]

Good job with the carbs.  Nice pics too.
I have a set of k6 carbs coming to me, this post will be very helpful. 

subscribed.

[MikeKato]

You got it for free? I saw it on CL and it was listed for 1k. The owner said he bought it brand new in 76 and I was contemplating on giving an offer but the miles scared me. I looked this morning and it said sold sold sold. I am really becoming fond of the 750's and am really diggin that color. Great buy though... I wish I had friends that were into these bikes...

Yes I remember that one also,In fact I just saw it yesterday in my garage. $900 took it.

5W05X25R23n53kd3lfb9oc225c056e09b14b2.jpg


"I wish I had friends that were into these bikes"

 I'm sure you'll find one,just hope he doesn't become too much of a pain in the *ss.

[hoodellyhoo]

Yes I remember that one also,In fact I just saw it yesterday in my garage. $900 took it.

Sweet. So what are your plans for the bike?

[hoodellyhoo]

Couple of new things to report. First, the airbox rubbers are still soft from soaking but have shrunk back down to their previous size. Some won't even stay in the airbox. I hear that ATF has something in it that causes rubber to swell a little (to keep seals soft) so maybe I will try soaking them in that and see where it gets me. I looked up how much new ones cost and it wasn't as bad as I thought so I may just go with new for peace of mind.

I've got two of the carbs cleaned. I noticed that the float valves for 2,3 and 4 are aftermarket (they don't have the small screen. Even though I usually only replace the gaskets I have  K&L rebuild kits and I might just replace all 4 float valves as long as I have them. Then at least they will all be the same. Also, some of the slow jets are pretty clogged. Nothing some old guitar strings can't handle.

The best news of today is that my new seat arrived!!! From the beginning I knew I wanted an oem seat. Not only does it look better but it's WAY more comfortable than that king/queen seat. The old seat pushed you so far forward that you had to use the highway pegs just to feel normal. Anyway, even though I'm trying to save money wherever I can and I could have found an old seat for cheaper, I did not want to go that route. Because I plan on having this bike for the long haul I didn't want to buy an old oem seat with 35 year old vinyl and foam that could fall apart soon. The problem is that the new reproduction seats are more than I wanted to spend. Thankfully forum member shouse76cb posted this barely used reproduction seat for sale. Now I have a basically new seat for less money. It looks soooo much better;D

[MikeKato]

Going to put the OM seat (very nice), pipes(pretty good),and tank(pretty good) away for a future project, when I try a cheap imitation of a restoration. Faring is coming off,different tank going on,fabricate side covers. Paint everything with that $18 paint I was reading about here on SOHC the other day,polish it up and ride the thing next year. 

Watching your build.
Good Luck!
Mike

[Johnie]

Gosh Trevor...I thought you loved the king/queen look??? That new seat looks great. Looks like you are coming along good. When you stopping over to see the K3? Have it in the patio now. Hunting this weekend, but after that come on over.

[hoodellyhoo]

Not much of an update to give but I finished cleaning the other two carbs today. Once they finish drying I'll assemble them, maybe sometime yet this week.